gprof reporting all 0.0 seconds

[Yang Zhang]

The output of gprof for my C++ program has no entries that contain non-0 
time:

   %   cumulative   self              self     total
  time   seconds   seconds    calls  Ts/call  Ts/call  name
   0.00      0.00     0.00 20347515     0.00     0.00  __gnu_cxx::__nor..
   0.00      0.00     0.00 18191192     0.00     0.00  __gnu_cxx::__nor..
   0.00      0.00     0.00 15330884     0.00     0.00  std::strchr(char..
   0.00      0.00     0.00 11405520     0.00     0.00  __gnu_cxx::__nor..
   0.00      0.00     0.00 10668361     0.00     0.00  __gnu_cxx::__stl..
   0.00      0.00     0.00 10173756     0.00     0.00  __gnu_cxx::__nor..
...

What's going wrong? The source (it's a simple 1-file program) and 
Makefile are available at:

http://assorted.svn.sourceforge.net/viewvc/assorted/hash-join/trunk/src/

In particular, the build command is:

g++ -Wall -lprofiler -lpthread -o hashjoin-pg hashjoin.cc -g -pg

Thanks in advance for any help.